adding weight to improve performance
 

(NVH performance)
About two months ago, I ordered 40 square feet of butyl based damping mat. So far, I've damped the door skins in all four doors, part of the hatch area and the rear wheelhouses. I also did the the door skin on the hatch.

I didn't take pictures for the door skin installs, but I did snap some pictures of the wheelhouse install.

I did two layers of mat in the doors with a third layer directly behind the speakers. I also purchased some 1/4" gauge closed-cell neoprene sponge rubber matting from the local rubber products distributor.

On a recent weekend I pulled out the back seat and all the plastic trim from the sides of the hatch and the plastic wheel house trims. I did one layer of damping mat in the areas that made the most "drumlike" noises when thumped. The areas of sheet metal that resonated at a higher pitch were left untreated.

I then cut sheets of the neoprene mat to sandwich in between the plastic interior trim and the sheet metal. Buttoned it all back up and down the road.

I've also damped part of the trunk floor with 3 layers of mat.

The first photo shows the damping mat applied to the sheet metal, the second photo the neoprene cut to fit and the third with the wheel house in place, the mat extends all the way into the area covered by the lower c pillar trim.

Has it made a difference? Most definitely. The resonance in the doors is greatly reduced. The bass from my speakers is much tighter. The noise from the god-awful FM-901's seems to come mostly from the front of the car now. None of the damping has made any difference in the drone from the mazdaspeed fart can (apparently resonates at the same frequency as the p5's cabin), but I'm whittling away at the noises. The doors close with more of a solid sound now. The next step is going to be to add neoprene matting to the back sides of the plastic door trim panels (have to buy more material and a fresh can of adhesive), and damp the spare tire well.
I forgot to mention I damped and neoprened the sheet metal under the rear seat, paying special attention to the resonant "hot" spot around and including the fuel sender. When it's all done I will have added about 19 lbs of mass to my car.

Pic shows the lower c pillar trim back in place.

Can you specify how much it costs for damping mat and where can we get some?

Sure. I purchased Damplifier damping mat from Second Skin Audio. The price is $96US for 40 square feet. You can order from their website at http://www.secondskinaudio.com/cgi-bin/index.cgi?p=hm